1. Field of the Invention
The present invention relates to furnaces of the type having combustion chambers for ignition of a fuel-air mixture and, in particular, to an oil fired heating furnace combustion chamber and mounting method therefor.
2. History
Heating furnaces typically include a combustion chamber for the burning of a fuel and air mixture therein, and a heat exchanger for efficient transfer of heat therefrom. The heat exchanger is generally designed to receive the passage of air returning from the space conditioned by the furnace (comfort air) and permit the air to pass over a region thereof in close proximity to the combustion chamber. In a fuel fired, forced air furnace, the combustion chamber is typically disposed within the heat exchanger. The heat from the combustion occurring therein, as well as the gaseous combustion products thereof, flow through a primary and, usually, a secondary heat exchanger to heat the comfort air flowing thereover. As the comfort air externally traverses this heat exchanger, combustion heat is transferred to the comfort air from the outer surface of the heat exchanger. The heated comfort air is then discharged from the furnace through ducts, or the like, for injection into the space from which it was originally withdrawn. This recirculation of air from and into a conditioned space is widely accepted as an efficient means for elevating and controlling the temperature therein.
The combustion chamber/heat exchanger assemblies for furnaces of the type described above are required to efficiently simultaneously perform two functions in an efficient manner. First, the combustion chamber must provide for essentially complete combustion of the fuel-air mixture received thereby. Secondly, the heat exchanger must also provide for efficient combustion heat transfer to the comfort air flowing through the furnace.
The genesis of the heat in a fuel-fired, forced air furnace is, of course, found in the combustion chamber where the fuel-air mixture is burned. It is therefore necessary for the combustion chamber to provide mechanical stability and functional efficiency during operation. The durability and reliability of conventional furnaces require that the combustion chamber be designed to effectively handle the requisite thermal distribution while presenting itself in a configuration that maximizes operational efficiency with a minimum of maintenance. At the same time, it is necessary that the combustion chamber be configured and aligned to promote stable combustion in a reliable fashion consistent with initial design parameters. For this to occur, the combustion chamber must be designed for maximum mechanical stability in shipping and handling and maximum thermal distribution in operation.
A variety of combustion chamber designs have found acceptance in prior art furnaces. Many of these designs are shown in a number of issued U.S. patents dating back to the late 1960's. For example, U.S. Pat. No. 3,470,864 entitled Combustion Chamber illustrates a generally cylindrical combustion chamber for an oil furnace in which an axially directed primary flame and combustion air are distributed radially and circumferentially through a series of circumferentially and axially spaced holes in the cylindrical combustion chamber wall. A pair of legs integrally formed of the ceramic material used to form the combustion chamber extends outwardly therefrom and engages a target plate forming an end wall of the heat exchanger. This pair of legs prevents the chamber from rotating and properly spaces the chamber from the target plate. The ends of the combustion chamber are supported by arcuate spring clips having outwardly bent ends. A number of specific design aspects have thus been considered relative to the combustion chamber and its assembly within the furnace.
Other patents illustrating prior art heat exchangers with cylindrical combustion chambers and/or combustion flame diffusers are shown in U.S. Pat. No. 4,203,415 entitled Heat Exchanger, U.S. Pat. No. 4,557,249 entitled Compact High Efficiency Furnace, and U.S. Pat. No. 4,718,401 entitled Hot Air Furnace. In the latter patent, the combustion chamber is constructed with an array of fins and includes a generally cylindrical, open ended diffuser preferably constructed of ceramic, or the like, and centered substantially coincident with a central axes of the burner for substantially enveloping a burning flame discharged therein. These specific combustion chamber configurations illustrate the wide variety of structural and functional parameters imposed upon combustion chamber assemblies. Of primary significance is, of course, the diffusion of the flame discharged within the combustion chamber and the thermal distribution of the heat generated thereby. Tantamount in the design, however, is also the mounting of the combustion chamber, the structural rigidity thereof, and the functional stability afforded by the design in operation.
As seen from the prior art references cited above, a variety of round and slotted openings have been used in prior art combustion chambers. A variety of combustion chamber mounting techniques have also been used. It is well known that the structural integrity of the combustion chamber relative to the remaining furnace necessitates a secure mounting configuration therein. Likewise the above referenced shape and size of the apertures as well as the spacing of the apertures in the combustion chamber or firebox necessitate long term structural and functional considerations.
It is necessary in the design of effective fuel fired, forced air furnaces for the combustion chamber to manifest efficient heat transfer and a stable structural configuration. For example, many conventional furnaces incorporate slotted apertures formed in elongate combustion chambers which are positioned within metal cages, and secured to adjacent panel walls of the combustion chamber assembly. Over the years, certain problems have been identified with such prior art designs. These problems include the inefficient circulation of combustion gases through the slots or apertures of the combustion chamber, the mechanical integrity of the combustion chamber material particularly around the slots or apertures therein and the stress, strain cracks that are often manifested therein. Additionally, access to the combustion chamber is often restricted due to its mounting configuration. This restricted access interferes with efficient repair and maintenance of the furnace as a whole.
Other considerations in combustion chamber design include the spacing of the opening in, through and around the combustion chamber and the basic thermal distribution aspects that are inherent in combustion chamber operation. Another equally serious problem, is the securement of the combustion chamber itself to a wall of the furnace housing. It is common for a combustion chamber formed of ceramic to be mechanically secured within a cage disposed within a heat exchanger in the furnace through the use of mechanical fasteners. Generally the cage extends rearwardly from a burner plate and captures the combustion chamber longitudinally thereagainst. A separate, permanent securement leg is often utilized to further stabilize the elongate combustion chamber relative to the burner plate against which it is initially secured. The support leg may, however, also interfere with certain gas flow patterns generated by the combustion chamber. A more serious problem is the position of the combustion chamber itself. Since it is often secured to a furnace panel wall by a metal cage and/or metal fasteners that extend along the elongate sides of the combustion chamber, any shrinkage of the ceramic material through normal use has been shown to cause a degree of separation of said combustion chamber from said panel wall. Any resulting separation is usually a deviation from initial design parameters and may permit a recirculating flow of combustion gases therearound. The recirculation of combustion gases back to a region within the combustion chamber may then result in less efficient combustion as well as related hot spots and functional inefficiencies due to the recirculation pattern of the hot gases.
It would be an advantage to overcome the problems of the prior art by providing a combustion chamber which may be mechanically secured within a furnace in a manner facilitating stability and reliability during operation as well as ease in accessibility to facilitate maintenance and repair. It would likewise be an advantage to provide a combustion chamber which also enhances the flow of combustion products therethrough and therearound for improving efficiency of the furnace. The present invention provides such a combustion chamber by utilizing a mounting collar which captures the combustion chamber at a first end adjacent the burner plate to which it is attached. The combustion chamber is also formed with a plurality of round holes formed in the side walls in a select pattern maximizing thermal distribution for particular applications and the circulation of combustion products outwardly therefrom. A mounting leg formed of combustible material is also secured to a second, opposite end of the combustion chamber for stabilization thereof during shipping and handling and disintegration during initial operation.